1. Field of the Invention
This invention relates to a prism for separating the illuminated light from a light source depending on the wavelength or polarized light components, a projection device for modulating the illuminated light radiated from the light source using a reflection type optical modulating element and for projecting the light to an enlarged scale using a lens and an optical component used in this prism and in the projection device.
2. Description of Related Art
For enabling display on a large sized screen, there has so far been known a projection device in which illuminated light is radiated from a lamp to a liquid crystal panel, on which a pattern consistent with input picture signals is displayed, and in which the illuminated light is modulated and reflected by the liquid crystal panel so as to be projected to an enlarged scale using a projector lens.
In this projection device, a polarized beam splitter (PBS) for separating the forward and return optical paths is provided in the optical path so that the optical path for the illuminated light towards the liquid crystal panel and that for the reflected light modulated by the liquid crystal panel will not be the same optical path. In this PBS 200, a pair of corner prisms 202, as substrates, are bonded together to hold a dielectric multi-layer film 201 in-between as shown in FIG. 1. Moreover, in this PBS 200, the dielectric multi-layer film 201 is formed to have different reflectance and transmittance values, depending on the wavelength or the direction of light polarization, and operates as a beam splitter for separating a light beam depending on the wavelength or the direction of light polarization.
The PBS 200 can be classified into a McNeill type in which the dielectric multi-layer film 201 separates the light beam depending on the polarized light component, and a dichroic type, in which the light beam is separated depending on the wavelength.
In the McNeill or dichroic type PBS, exploiting the interference of multi-layer dielectric films, the performance is determined by the refractive index of the substrate and the combination of the layered dielectric materials, so that the performance beyond a certain limit cannot be achieved. In such PBS, it is extremely difficult to maintain separation characteristics between the P-polarized light and the S-polarized light over a wide angle of incidence. Thus, if this PBS is built into an optical system with a large angular distribution, that is with a small F-value, light separation characteristics as well as the light exploitation efficiently is lowered.
As a solution, a flat plate shaped diffraction grid PBS 210, shown in FIG. 2, may be used. In this diffraction grid PBS 210, a diffraction grid 212 of e.g., aluminum is provided on a glass substrate 211. By this diffraction grid 212, light is separated depending on polarized components. However, if the grid is used as a beam splitter, the diffraction grid PBS 210 needs to be arranged obliquely relative to the main light beam, so that, if the diffraction grid PBS is inserted into the optical path, astigmatic aberration is produced.
In the case of the McNeill or dichroic prism, distortion is produced in the prism due to temperature rise in the prism or by a holding mechanism, so that diffraction distribution in the substrate becomes nonuniform with the result that phase difference is produced in the light transmitted through the substrate and hence the extinction ratio is partially lowered. With the projection device, employing this prism, so-called black spots are produced in the projected image such that clear images cannot be projected.
Thus, as a prism substrate, such a material having a low modulus of opto-elasticity and less susceptible to distortion in the prism needs to be selected. However, a material having a low modulus of opto-elasticity is costly, such that the prism employing the low modulus of opto-elasticity or the projection device employing such prism is expensive. On the other hand, it is extremely difficult to produce a prism of high performance from an inexpensive vitreous material having a high modulus of opto-elasticity.
In view of the above-depicted status of the art, it is an object of the present invention to provide a prism or an optical component, in which astigmatic aberration is suppressed and which has uniform distribution of the modulus of elasticity in the substrate, and a projection device employing such prism or optical component.
In one aspect, the present invention provides a prism for transmitting or reflecting incident light depending on polarized light components thereof, including a substantially grid-shaped diffraction grid, formed of metal, a pair of diffraction grid substrates sandwiching the diffraction grid in-between, an adhesive layer provided on each surface of each diffraction grid substrate facing the diffraction grid, and a pair of block members secured through the adhesive layer to each of the paired diffraction grid substrates, wherein a medium having a refractive index approximately equivalent to that of the block members is charged in a gap defined between the diffraction grid and the paired grid substrates.
With the prism of the present invention, the diffraction grid is sandwiched between a pair of the block members to suppress the astigmatic aberration in the image-forming optical system. The incident light may be transmitted or reflected depending on the polarized light components as optimum polarized light separation characteristics are maintained over a wide angle of incidence.
In another aspect, the present invention provides a projector device including a light source for radiating illuminated light, a light collecting lens for collecting the illuminated light radiated from the light source, a prism for transmitting or reflecting the light from the light collecting lens depending on polarized light components thereof, a light modulating element for modulating the illuminated light transmitted or reflected by the prism and for reflecting the modulated light, and a projector lens for enlarging and projecting the reflected light reflected or transmitted by the prism and modulated by the light modulating element, wherein the prism includes a substantially grid-shaped diffraction grid, formed of metal, a pair of diffraction grid substrates sandwiching the diffraction grid in-between, an adhesive layer provided on each surface of each diffraction grid substrate facing the diffraction grid, a pair of block members secured through the adhesive layer to each of the paired diffraction grid substrates, and a medium having a refractive index approximately equivalent to that of the block members, the medium being charged in a gap defined between the diffraction grid and the paired grid substrates.
With the projection device of the present invention, when the reflected light modulated by the optical modulation element is transmitted through or reflected by the prism, the image of the reflected light may be projected as reflected light is optimally separated into polarized light components and as astigmatic aberration is prevented from occurring.
In still another aspect, the present invention provides an optical component in which the light of preset polarization state is transmitted and radiated, wherein plural plate shaped members, having the surfaces polished to mirror finish, are layered together with interposition of soft type adhesives.
With this optical component of the present invention, in which the plural plate shaped members are layered together with interposition of soft type adhesives, the internal stress produced by strain may be suppressed to maintain the refractive index distribution constant to permit light to be transmitted without disturbing the state of polarization.
In another aspect, the present invention provides a prism including a light separating layer provided on a plate-shaped substrate and having the properties of transmitting or reflecting light depending on polarized light components, a pair of adhesive layers on both surfaces of the plate-shaped substrate provided with the light separating layer, and a pair of block members sandwiching the light separating layer with the adhesive layer in-between, each block member being a plurality of plate shaped members having surfaces polished to a mirror finish, the plate shaped members being alternately layered with soft type adhesive in-between.
With the present prism, in which the light separating layer is sandwiched with block members comprised of plural plate shaped members layered together with interposition of soft type adhesive layers, the incident light may be transmitted or reflected depending on the polarized light components and radiated without disturbing the state of polarization under suppression of astigmatic aberration.
In yet another aspect, the present invention provides a projector device including a light source for radiating illuminated light, a light collecting lens for collecting the illuminated light radiated from the light source, a prism for transmitting or reflecting the light from the light collecting lens depending on polarized light components thereof, a light modulating element for modulating the illuminated light transmitted or reflected by the prism and for reflecting the modulated light, and a projector lens for enlarging and projecting the reflected light reflected or transmitted by the prism and modulated by the light modulating element, wherein the prism comprises a light separating layer provided on a plate-shaped substrate and having the properties of transmitting or reflecting light depending on polarized light components, a pair of adhesive layers on both surfaces of the plate-shaped substrate provided with the light separating layer, and a pair of block members sandwiching the light separating layer with the adhesive layer in-between, each block member being a plurality of plate shaped members having surfaces polished to a mirror finish, the plate shaped members being alternately layered with soft type adhesive in-between.
With the projection device of the present invention, when the light modulated by the optical modulating element is modulated and reflected, the reflected light may be optimally separated into respective polarized light components, while the image is projected by the projector lens under suppression of astigmatic aberration.
With the present prism, a light beam may be optimally separated over a wide angle of incidence, while the astigmatic aberration may be suppressed even if the prism is used in the image-forming optical system. Since desired characteristics of the prism may be achieved without using the substrate of a high refractive index, by reason of the superior separation characteristics, it is possible to realize a favorable performance at the same cost as compared with the PBS by the dielectric multilayer film. Since it is unnecessary to use a substrate of a high refractive index, it is possible to reduce the cost and the weight. The present prism may be used in a variety of optical systems in view of the high degree of freedom in combining different materials of the constituent elements which lead to desired characteristics.
Since the soft type adhesive is provided between the grid substrate and the prism substrates, it is possible to suppress the internal stress and optical distortion. Additionally, since the prism substrates are comprised of flat plate shaped members optically combined with interposition of a soft type adhesives, it is possible to further reduce internal stress and optical distortion.
With the projector device, employing the present prism, separation characteristics may be maintained at a high NA and hence a bright image of high contrast may be produced, while the light utilization efficiency may be improved. Since the astigmatic aberration in the image-forming optical system may be suppressed with use of the present prism, a bright image may be projected. Moreover, with the use of the present prism, the cost and the overall weight of the device may be reduced.
Since the prism allows to reduce optical distortion, it is possible to suppress black spots in the projected image and distortion otherwise caused by the thermal stress and to reduce the effect of heat otherwise produced by increasing the volume of light incident on the prism, with the consequence that the volume of light radiated from the light source may be increased to increase the brightness of the projected image.
The present optical component may be divided into plural plate-shaped members and soft type adhesive layers may be interposed in the interface region. Thus, the stress applied to the interface region may be relieved by the soft type adhesive layers to suppress possible optical distortion.